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Network and Internet Support of Software Layer

The OSI network model layers are arranged from the lower levels starting with the hardware to the higher levels.
  1. Physical Layer: The actual hardware.
  2. Data Link Layer: Data transfer method puts data in frames and ensures error free transmission. Also controls the timing of the network transmission. Adds frame type, address, and error control information.
    IEEE divided this layer into the two following sublayers.
  3. Logical Link control (LLC): Maintains the Link between two computers by establishing Service Access Points (SAPs) which are a series of interface points.
  4. Media Access Control (MAC): Used to coordinate the sending of data between computers. The 802.3, 4, 5, and 12 standards apply to this layer. When discussing the MAC address of a network card, they are referring to the hardware address of the card.
  5. Network Layer: IP network protocol. Routes messages using the best path available.
  6. Transport Layer: TCP, UDP. Ensures properly sequenced and error free transmission.
  7. Session Layer: The user's interface to the network. Determines when the session is begun or opened, how long it is used, and when it is closed. Controls the transmission of data during the session. Supports security and name lookup enabling computers to locate each other.
  8. Presentation Layer: ASCII or EBCDEC data syntax. Makes the type of data transparent to the layers around it. Used to translate date to computer specific format such as byte ordering. It may include compression. It prepares the data, either for the network or the application depending on the direction it is going.
  9. Application Layer: Provides services software applications need. Provides the ability for user applications to interact with the network.

Software Defined Networks
The client clicks a link or enters text; HTML generates a request message to be sent over the internet.

Internet protocols (TCP/IP) encode and transmit the request message over the internet. Software on routers throughout the internet use an IP address to keep forwarding the message to its intended recipient.

Web server software receives and reassembles the request message and gathers data from other documents and database applications for the response. Web server software assembles the packet of files to be sent back to the client.

Internet protocols (TCP, IP) encode and transmit the response message packet over the Internet. Software on routers throughout the Internet use the IP address in the header of the message to continue forwarding the response message packet to the intended recipient.

The client's computer receives the response message packet of new information of documents and displays them in a web browser, using HTML.